This invention relates to a structural beam, particularly for a vehicle such as an automobile or truck, and to an improved beam construction and an improved process for manufacture thereof.
Automotive vehicles such as automobiles and trucks employ a significant number of different structural beams associated with the vehicle frame to provide strength and rigidity. Many such beams are intended to provide increased protection for the vehicle occupants in the event of a collision or other accident. For example, a conventional door for a vehicle such as an automobile or truck has a hollow frame with vertical side rails, a bottom rail and a top rail. A structural door intrusion beam is typically disposed interiorly of the frame at a location spaced upwardly from the bottom rail and extends generally horizontally between and has opposite ends fixed to the side rails. The door intrusion beam thus provides improved strength against side impact on the vehicle door so as to provide improved protection for a passenger in the event of a collision. The door intrusion beam is desirably constructed of a material and/or configuration so as to maximize its strength and effectiveness in the event of a collision. There is, however, a continuing need to improve manufacturing processes to permit the beam to be formed in an economical manner while at the same time providing a beam having desirable impact strength while at the same time minimizing weight.
Numerous beam constructions and manufacturing processes have been developed or formulated in order to attempt to provide a strong intrusion beam, and in particular permit manufacture of a strong intrusion beam from less expensive materials, and in this respect intrusion beams have been developed which involve a wide variety of cross sections, including beams wherein the main elongate beam body has a hat-shaped cross section, an H-shaped cross section, a longitudinally grooved cross section, a hollow tubular cross section, and other complex cross-sectional shapes. In these known beams, the main elongate beam body is provided with flanges at opposite ends which are suitably shaped to enable them to be fixedly secured to the side frames of the door, which fixed securement preferably involves welding. Such flanges are thus preferably of lower grade or lower strength steel in view of the difficulty of welding high strength materials. Hence, many of the known intrusion beams have necessarily involved a multi-piece construction, namely an elongate beam body of one material or shape so as to provide one property, and separate flanges of a different material or property to facilitate attachment to the door frame. These beams and the manufacturing processes affiliated therewith are typically of greater complexity and cost than is desired.
For example, in one known construction, the elongate beam body is formed as a hollow tubular member which is roll-formed to define an elongate tubular element, with the material used for forming the roll-form being of lower strength. Following roll-forming and welding, the elongate sheet is then subjected to intermittent heating and quenching at selected lengths therealong so as to provide for strength increases in the element at selected locations. The element is cut to length to define a beam part. Separate preformed end flanges of lower strength steel are then welded to the ends of the elongate center beam body, which ends have not been heat treated. This overall forming process is, however, unnecessarily complex due to the way in which the quenching of the roll-formed tubular section is heat treated in an intermittent manner at select locations, which also causes loss in strength adjacent the beam ends, and wholly separate end flanges are separately manufactured and thereafter secured to the ends of the tubular beam.
Examples of various door intrusion beam constructions, and the manufacturing processes therefor, are illustrated by U.S. Pat. Nos. 4, 090, 734, 4,599,843, 4,708,390, 4,838,606, 5,080,427, 5,124,186, 5,232,261, 5,272,841, 5,370,437, 5,404,690, 5,466,032, 5,540,016, 5,600,931, 5,756,167, 5,785,376, 5,813,718, 5,813,719, 5,868,456, 5,884,960, 5,887,938.
Vehicles such as automobiles and trucks also employ numerous other types of structural beams for defining part of the vehicle for structural and/or safety purposes, and examples of such beams are bumpers, roof bows, etc. These beams desirably provide high strength, but the need to provide weldable mounting flanges often compromises the selection of beam material and the overall strength of the beam, thus resulting in undesired increases in beam size and/or wall thickness, and consequent increases in weight.
Accordingly, it is an object of this invention to provide an improved method of manufacturing a structural beam for a vehicle, and an improved beam structure, which in one embodiment comprises a door intrusion beam, and which improves on and overcomes many of the constructional or processing disadvantages associated with conventional processes and constructions.
More specifically, the present invention relates to an improved structural beam, particularly for a vehicle, which possesses an elongate tubular beam part which at opposite ends is provided with suitably shaped mounting flanges for securement to a vehicle frame. The elongate tubular beam part and the flanges provided at opposite ends thereof are all defined by an integral, one-piece, monolithic steel structure which has been initially roll-formed from an elongate flat metal sheet so as to define the closed tubular structure of the tubular beam part, and which has been subjected to heating and quenching so that the elongate tubular beam part is of relatively high strength steel throughout its entire length, whereas the integrally and monolithically joined end flanges remain as lower strength steel which has been significantly unaffected by the heat treatment and quenching so as to permit appropriate shaping thereof and ease of welding to the vehicle frame. This beam is particularly desirable for use, for example, as a door intrusion beam, a roof bow beam, or an exterior vehicle bumper.
The present invention also relates to an improved process for forming the structural beam, as aforesaid, which process involves forming beams by providing an elongate sheet of relatively flat low-strength steel, subjecting the sheet to appropriate notching and/or slitting operations in those areas of the sheet which will ultimately be formed into the end flanges, then feeding the elongate sheet through a roll-forming mill so that the sheet is transversely deformed (i.e. rolled) into an elongate profile having a reshaped cross section which includes a substantially closed tubular cross section which extends along the. un-notched region of the sheet to define the elongate center tubular beam part, with the notched regions of the sheet failing to define a closed tubular section due to the presence of the notches. The roll-formed profile is supplied to an induction heater followed by a quencher to effect heating of solely the closed tubular section so that this section, when quenched, results in the elongate tubular beam part being of relatively high strength. The heating and quenching, however, is ineffective in significantly modifying the properties of the notched regions, and hence they retain their lower strength. These regions are then suitably shaped to define the desired end flanges, which are integrally and monolithically joined to opposite ends of the high-strength elongate tubular beam part, whereupon the finished structural beam can be more easily welded to the vehicle frame, and the flanges also more readily accommodate tolerance variations and distortions which are typically experienced with respect to the frame.
The process of the present invention, as briefly summarized above, preferably effects notching of a substantially continuous sheet at defined intervals therealong to define notched and un-notched regions in a defined arrangement lengthwise along the sheet, with the sheet thereafter being roll-formed to define said profile as an elongate and continuous structure which is still joined to the flat steel sheet. Abutting or contacting edges of the sheet at least through the closed tubular sections are then welded together, and the continuous profile thereafter sequentially moved into and through the induction heater and the quencher. The elongate profile is, after quenching, transversely cut or severed at the notched region to define separate beams having end flanges at opposite ends thereof as defined by the notched regions. The end flanges can be appropriately reshaped, if necessary, as by stamping or the like, to provide the desired configuration.
The improved beam of this invention, and the improved process for forming the beam, both as summarized above, according to a preferred embodiment relate to a door intrusion beam for a vehicle door, whereas alternate embodiments relate to a roof bow beam for a vehicle roof or a vehicle bumper beam.